In a hatchery there are many factors that need to be optimised to maximise chick quality. Besides the design of the incubator, the incubation process and factors such as eggshell temperature and carbon dioxide concentration affect embryo development and, therefore, chick quality and subsequent performance.
By Dr. Inge van Roovert-Reijrink, HatchTech, Veenendaal, The Netherlands
Besides optimising hatchability, an important goal of a hatchery is to deliver perfect day-old chickens. To optimise chick quality it is important to have a good method to measure chick quality. A method to evaluate the incubation process and to predict subsequent performance is chick length. Chick length is determined by stretching the chick along a ruler and measuring the length from beak to the end of the middle toe. This length is positively related to the yolk free body mass (body weight without the residual yolk weight) of the chicken, which indicates how much yolk is converted into body development during incubation.
To optimise chick quality, many factors need to be taken into account. Already before the egg is laid, chick quality can be affected by breeder genetics, breeder flock age, and breeder flock health. Furthermore, after the egg is laid, nest hygiene and storage conditions at the breeder farm affect egg quality, embryo viability, and chick quality. Breeder farm management determines partly whether a hatchery can deliver perfect day-old chickens.
Incubator design and eggshell temperatures
During incubation, all eggs in the incubator require the optimal eggshell temperature for optimal embryonic development. Too high or too low eggshell temperatures will negatively affect chick quality and uniformity. To obtain optimal and uniform eggshell temperatures throughout the incubator, the design of the incubator is crucial. The air velocity has to be the same throughout the incubator because variation in air velocity creates variation in heat transfer capacity of the air and consequently variation in eggshell temperatures.
Relative humidity is also an important component of heat transfer. Humid air transfers heat better than dry air. To maintain optimal eggshell temperatures throughout incubation, it would be ideal to maintain a high relative humidity during the whole incubation process. During the first nine days of incubation, when embryonic heat production is low, the heat from the surrounding air is more easily transferred to the embryo when relative humidity is high. After nine days of incubation, when embryonic heat production increases exponentially, the heat from the embryo is transferred more easily to the surrounding air when relative humidity is high. However, a high relative humidity during the whole incubation process is impossible because an egg needs to lose at least 10% of its weight at day 18 of incubation to maximise hatchability. Therefore, a balance must be found between relative humidity to control heat transfer (to maintain uniform eggshell temperatures) and relative humidity to control egg weight loss.
Studies are performed to determine the optimal eggshell temperature during incubation. Several studies have shown that the best chick quality is obtained when the eggshell temperature is maintained at 37.8°C (100°F) during incubation. Eggshell temperatures lower or higher than 37.8°C (100°F) during the first and third week of incubation result in a higher percentage of second grade chickens (up to 5% more) and smaller chickens (up to 5 mm smaller). We showed that eggshell temperatures of 38.9°C from day seven of incubation onwards, increased the incidence of ascites in later life.
The optimal eggshell temperature during the hatching process is hardly investigated. It is known that the percentage of second grade chickens increased with 2% when the eggshell temperature was 38.9°C instead of 37.8°C during the last week of incubation. This showed that high eggshell temperatures during the hatching process also negatively affect chick quality. It is difficult to obtain optimal requirements for all embryos during the hatching process because embryos and chickens can be in different phases of the hatching process at the same time: internal pipping, external pipping, hatched and wet, hatched and dry.
Uniform eggshell temperatures in the setter and hatcher are crucial to minimise the variation in embryonic development. When variation in embryonic development is minimised, optimisation of environmental conditions in the hatcher, according to the embryo's requirements, will be easier.
Carbon dioxide concentrations
In commercial hatcheries, the carbon dioxide concentration is often maintained below a maximum level to supply enough fresh air and oxygen to the developing embryos. Some scientists have investigated the effect of high carbon dioxide concentrations at several time frames during incubation on embryonic development and chick quality. A gradual increase of carbon dioxide to a concentration above 1% during the first 10 days of incubation, has a positive effect on relative growth during the first week of life, but does not result in higher body weights at slaughter age. Chicken embryos however can tolerate high carbon dioxide concentrations (4%) between day 10 and 18 of incubation without an effect on chick quality.
In practice, some hatchery managers try to reduce the hatch window (time between the first and last chicken hatched) by reducing the inlet of fresh air into the hatcher. A reduction of the ventilation rate can increase carbon dioxide concentrations in the hatcher above 0.8%. Carbon dioxide concentration in the air cell will increase as well and this triggers the embryo to hatch earlier than if the maximum carbon dioxide concentration is below 0.35%. Due to the high carbon dioxide concentration, chickens hatch earlier, but the effect of a high carbon dioxide concentration during the hatching process on chick quality is unknown and might be negative.
In some commercial incubators, the cooling capacity of the incubator can partly depend on the inlet of fresh air. In such incubators, a reduction of the ventilation rate results in too high eggshell temperatures. Eggshell temperatures of 38.9°C during the last week of incubation have a negative effect on chick quality. A combination of high eggshell temperatures and a high carbon dioxide concentration during the hatching process might be even worse for chick quality.
Conditions after hatch
From the moment of hatch until delivery at the broiler farm, rectal temperatures of chickens have to be maintained between 40.0 and 40.6°C. At higher temperatures, chickens start panting to cool their body by evaporation. Panting can result in dehydrated chickens in a period chickens have no access to feed and water. Overheating after hatch has a major effect on subsequent growth performance and mortality. Design of hatchers, chick handling rooms, and trucks is, therefore, crucial in achieving the correct environment for every single chicken from hatch until delivery at the broiler farm.
Eggshell and rectal temperatures
To obtain maximum chick quality, uniform and optimal eggshell temperatures throughout incubation are crucial. Incubator design, air velocity, and relative humidity have to be taken into account to achieve uniform and optimal eggshell temperatures throughout incubation.
Chicken embryos seem to tolerate high carbon dioxide concentrations until day 18 of incubation. However, the effect of high carbon dioxide concentrations during the hatching process on chick quality is unknown. A reduction of the ventilation rate in the hatcher is not advisable because this can increase eggshell temperatures, which negatively affects chick quality.
To maintain chick quality after hatch, rectal temperatures of chickens should be maintained between 40.0 and 40.6°C from hatching until delivery at the broiler farm.